The present invention concerns a method for recovering synthetic waste material contaminated with other materials, by means of a chemical treatment consisting of impregnating the materials with a substance which attacks the contaminant material but is substantially neutral toward the synthetic material, and a simultaneous mechanical treatment consisting of tumbling the loose, uncrushed waste material in a hermetically sealed drum.
The synthetic waste material is usually contaminated with other materials such as one or more dyes, printing ink, metal coatings, paper or other types of tags, glue, etc. "Clean" recycling requires that the synthetic base material be free of contaminants before re-use.
Current attempts to recover such material consist of a chemical treatment during which the waste is submerged in an aggressive solution for a variable length of time in order to neutralize the contaminant material. During such treatment the solution impregnates synthetic material, which is thus partially degraded and often cannot be used again.
As the price of base materials increases, recycling synthetic materials becomes more and more important. The polycarbonate used in the manufacture of optical character reading disks is one of the more desirable materials to recycle.
Various attempts have been made to recycle polycarbonate and other synthetic materials. One such example is described in German Patent Application No. DE A 85 11 711, which describes a method of recovering synthetic waste from optical character reading disks wherein the previously crushed waste is submerged in a chemical bath consisting of several substances with solvent properties.
U.S. Pat. No. 4,802,048 describes a method for treating pieces of synthetic material coated with at least one layer of a macromolecular organic polymer, wherein the particles are first finely ground and then tumbled in a caustic soda solution. The mixture consists of 25% solid material and 75% alkaline solution.
A major drawback with all these known methods is that the previously ground or microminiaturized material for recycling is immersed in an aggressive solution, which, while successfully removing the unwanted material, also impregnates the material to be recycled.